DRM Overscan margins handling

At Raspberry Pi we're still having to handle displays that overscan the image, discarding a chunk of border. DRM supports the 4 margins properties on connectors that perform automatic scaling to account for this.

With xrandr you can use the --set command to set arbitrary DRM properties. Has there been any similar consideration been made under wlroots/Wayland to handle overscan or other DRM properties?

Another option is that it could be done directly as part of the composition instead of passing it off to the DRM properties, rendering to a framebuffer that is smaller than the full screen size, and/or passing in a destination rectangle smaller than the full display mode.

"Broadcast RGB" is also a common DRM property to handle displays that don't pay attention to the HDMI AVI Infoframe correctly, and require the link to be forced to either limited or full range. That one can't be emulated during composition and does need to be passed into DRM.